Today radio performance typing of the present generation of base stations according to standard requirements (for instance GSM, PDC and DCS) is performed by measurement in an antenna reference point. This point is defined by the current standard and is constituted by the antenna connector terminal and should regarding transmission be located after active electronics, but regarding reception be located before the electronics.
When utilizing active antennas having distributed amplifiers this approach leads to problems. Each transmitter and receiver module, respectively, is connected to one or more antenna elements and the merging of the signals takes place in the air. For this type of antennas a new type of antenna reference point must be defined.
One method of measurement could be to individually measure each radiating element interface and state a type acceptance for each unit as such. This would lead to a very large number of measurements and produce a result which would not be representative for the signal environment resulting of the merging in the air. The position in space and relative amplitudes of spuriouses and main signal will not be measured, however this is entirely of vital importance for the resulting signal representation.
Another method is to measure radiation pattern by means of an antenna test range. This method is very difficult as it is necessary to maintain a safe control of undesired disturbance sources. That is practically impossible as certain measurements are performed at signal levels of -110 dBm and less. If the measurements are performed in an unshielded room or outdoors it will be disturbed by present active mobile telephones and when performing transmit tests, telephone systems operating in the neighborhood may be disturbed by such a test.
There will be found a number of documents relating to calibration of phased array antennas, for instance U.S. Pat. No. 5,063,529 disclosing utilization of automated processing techniques to compute calibration coefficients based on a generalized model of the array. However the documents relating to such calibrations are not dealing with systems having active antennas with distributed amplifiers.
Therefore there is a large need for a new method for performing a reliable test method for an active antenna system containing distributed amplifiers for instance for use in base stations for radio telephone systems like GSM, PDC or DCS.